Add keys to jump to latest/oldest unread (#214)

* Key to jump to latest/oldest unread #186

Latest/oldest unread/highlight.
Default bindings match the bindings for previous/next unread/highlight.

Allows the user to read messages in the order of receiving them.
Or the opposite order, to stay on top of things.

* Clean up code

Use let instead of var, and proper indentation

* Fix case for some variables in RoomList.qml

Some variables were using snake_case instead of camelCase like usually
done in QML code (note that the model items come from python)

Co-authored-by: miruka <miruka@disroot.org>

src/config/settings.py

@@ -357,6 +357,10 @@ class Keys:
         previous_unread = ["Alt+Shift+U"]
         next_unread     = ["Alt+U"]
 
+        # Switch to the room with the oldest/latest unread message.
+        oldest_unread = ["Ctrl+Shift+U"]
+        latest_unread = ["Ctrl+U"]
+
         # Switch to the previous/next room with highlighted messages in the
         # list. What causes a highlight is controlled by push rules
         # (editable in GUI account settings): by default, this includes
@@ -364,6 +368,11 @@ class Keys:
         previous_highlight = ["Alt+Shift+M"]
         next_highlight     = ["Alt+M"]
 
+        # Switch to the room with the oldest/latest unread message,
+        # but only rooms with highlights are considered.
+        oldest_highlight = ["Ctrl+Shift+M"]
+        latest_highlight = ["Ctrl+M"]
+
         class AtIndex:
             # Switch to room number X in the current account.
             # Each property is a list of keybinds for the room number X: